The invention relates to a method for securing the intermediate time periods required at an intersection in a street traffic signal system, and to an apparatus for practicing such method. The term "intermediate times" as herein employed is intended to include all protective time periods at a signal-controlled street intersection to prevent the possibility of accidents resulting from the varying geometry of the different crossings and varying speeds of the pedestrians and vehicles.
To this end, at the end of a green light of one flow of traffic, the flows of all traffic antagonistic thereto, irrespective of whether such antagonistic traffic flows relate to vehicular or pedestrian traffic, the following new traffic flow may be released only after all traffic participants of the traffic flow just stopped have cleared the intersection. However, as the prerequisites of such intermediate protective times, namely the geometry of the individual intersections and/or the differential speeds of pedestrian and vehicle flows, do not vary, the intermediate protective periods need be determined only once, after which they shall not be varied either by faulty equipment or by intervention of unauthorized parties.
The invention is directed to the problem of assuring a compliance with both of these requirements, more particularly to immediately indicate any occurring discrepancies in intermediate protective times and, in the event thereof, to introduce corresponding safety measures, and in addition to also make it impossible for authorized maintenance personnel to make any change in the intermediate periods.
This objective is achieved in accordance with the invention in a method which involves the following steps:
(a) Upon the end of the green light period of each individual signal of the respective traffic flows to be controlled independently, the immediately following time period is totalled. PA0 (b) Such "actual values" are then respectively compared with "theoretical values" for the traffic flows antagonistic to the green light signal to be connected, and upon the actual value attaining and/or exceeding the prescribed theoretical time values, the associated command signal to connect such green light signal is released. PA0 (c) All theoretical values are added at intervals somewhat smaller than that corresponding to the time rhythm of the traffic signal system, in effect forming an additional "actual value", which is then compared with a corresponding "theoretical value", and in the event of a discrepancy therebetween, appropriate safety precautions are released.
In an additional improvement of the invention, a block, for example in the form of code words, must be provided to introduce or change the theoretical values for the individual intermediate time periods, and such block must be initially eliminated to ready the system for a change therein.